The present invention relates to an ion laser tube, and more specifically to a structure of a discharge path within an elongated airtight envelope.
In an ion laser tube, laser oscillation is caused by energy transition owing to ionization of a gaseous active medium such as argon and krypton. In order to obtain a higher output power, ion density should be increased. To this end, it is necessary to supply a large electric current of more than ten amperes in a narrow discharge path having an inner diameter of 1 to 4 mm.
However, oscillation efficiency of the ion laser tube is low. Namely, most of applied electric energy is converted to heat, and thus the discharge path member or laser capillary reaches an extremely high temperature. Therefore, the material for forming the laser capillary requires high durability to the high temperature plasma.
Furthermore, the large amount of heat will cause a deformation of a laser tube so that the optical quality of the generated laser beam is greatly deteriorated. In addition, if the deformation of the laser tube becomes too great, the laser tube itself will often be broken.
Therefore, it has been an ordinary practice to provide a cooling mechanism to the laser tube. In such laser tube provided with a cooling mechanism, the envelope and the laser capillary require high thermal conductivity in addition high durability to plasma.
According to our research, we have found that aluminum nitride (AlN) is superior to previously used material such as graphite, tungsten and beryllia from the viewpoint of satisfying all conditions of high thermal conductivity, high durability to plasma, ease of processing and fabricating that dominates the cost, and steady procurement. However, when AlN is used to form the laser capillary, the sputtering by plasma bombardment resolves the AlN capillary to produce nitrogen gas. The discharge condition of the laser tube is affected by the nitrogen gas and output power becomes unstable. Eventually, the termination of the discharge will occur.